1. Field of the Invention
The present invention relates to fuel injectors for internal combustion engines, and particularly to fuel injectors which produce improved fuel economy, noise reduction, and reduction of undesirable exhaust emissions, including smoke, oxides of nitrogen, and hydrocarbons, and which avoid further and uncontrolled injections in the event of nozzle failure.
2. Description of the Prior Art
Accumulator-type fuel injectors have been known in the art for many years, but never have achieved widespread use. It is believed this is because they have heretofore not solved problems present in conventional injectors, and have even introduced additional problems which have been inherent in prior art forms of accumulator injectors.
One serious problem with both conventional fuel injectors and prior art accumulator-type fuel injectors has been premixed burning of the fuel. Typically, about 25-50 percent of the total quantity of fuel injected will be atomized and mixed with air prior to the start of combustion. The sudden combustion of this premixed fuel causes a rapid rate of heat release at the beginning of ignition, with a resulting excessively high noise level, and undesirable exhaust emissions including oxides of nitrogen. One answer to this problem is to provide a two-stage injection event, with a small pilot charge of fuel first injected and ignited, and then the main charge of fuel injected and immediately ignited by the already ignited pilot charge. A system of this type is taught in Loyd U.S. Pat. No. 4,414,940. Although the Loyd system does solve the problem, it requires two separate injectors, one for the pilot charge and another for the main charge, making the system undesirably complicated and expensive.
Intensified fuel injectors typically rely on a balancing of pressures in the high pressure chamber and accumulator chamber or other chamber supplied with fuel from the high pressure chamber to terminate an intensification stroke. However, in the event of injector nozzle breakage, cracking or other failure, the balancing pressure may be relieved from the accumulator chamber or other downstream chamber since the injector needle cannot effectively close off the nozzle, and fuel can continue to flow into the needle cavity from the high pressure chamber, and thence out through the breach. Without a safety feature to prevent further flow of fuel through the high pressure chamber, the result could be a series of further and uncontrolled injection events.